1. Field of the Invention
The present invention relates to a method and apparatus for reproduction on magnetic tape by using rotary drum heads which is used for example, in a digital audio tape recorder of rotary head system (R-DAT).
2. Description of the Prior Art
The apparatus for recording/reproducing audio signals converted into digital signals or digital data in a magnetic tape has been realized. In such apparatus, in order to increase the quantity of data recorded on a magnetic tape, magnetic heads differing in azimuth angle are attached to a rotary drum, and the magnetic tape is scanned while rotating the rotary drum so as to record/ reproduce the data.
FIG. 1 shows a track pattern of a magnetic tape 1 in which data is written in such manner. A track Ai (i=0, 1, 2, . . . , n) is, for example, composed of the data written through a magnetic head possessing a positive azimuth angle, and a track Bi is composed of, for example, the data written through a magnetic head having a negative azimuth angle.
To reproduce in the normal direction, the rotary drum is rotated in the direction of arrow 13 on a magnetic tape 1 running in the direction of arrow 11. The magnetic head having the positive azimuth angle and the magnetic head having the negative azimuth angle alternately scan the tracks Ai, Bi, and read out the data written in the track Ai, Bi. Therefore, the data written on the magnetic tape 1 are reproduced in the sequence of tracks A0, B0, A1, B1, . . . , An, Bn. Such reproduced signals are led out as shown in FIG. 2 (2).
Usually, a set of tracks Ai, Bi makes up one frame Fi. Rearrangement of data sequence in recording of the data on the magnetic tape 1, that is, the so-called interleaving, is complete within this one frame. Accordingly, the reproduced data is processed in the unit of one frame.
A processing circuit for processing the reproduced data distinguishes a pair of tracks composing one frame, on the basis of the track identification signal obtained by detecting the rotation of the rotary drum. This track identification signal is, as shown in FIG. 2 (1), at high level when the data of the track Ai, for example, is reproduced, and at low level when the data of the track Bi is reproduced. The processing circuit processes the reproduction signals which have been led out in the high level period of the track identification signal and in the low level period succeeding this high level period, as the data of one frame.
In this way, the magnetic tape reproducing apparatus can correctly process the data of tracks Ai, Bi composing one frame Fi.
In such magnetic tape reproducing apparatus, when reproducing in the reverse direction by running the magnetic tape in the direction indicated by arrow 12, the signal led out from the magnetic head is shown in FIG. 3 (2). The track identification signal at this time is as shown in FIG. 3 (1). The processing circuit for processing the reproduced signals recognizes the reproduced signals which have been led out in the high level period of the track identification signal and the low level period succeeding the high level period as one frame, and therefore in the reproduction in the reverse direction, it may. be misunderstood that the tracks Ai+1 and Bi compose one frame. In such apparatus, hence, normal reproduction action in the reverse direction cannot be effected.